The present invention relates to pneumatic nail guns, and particularly to a pneumatic nail gun having a movable cylinder for a hitting piston of the nail gun driven by the high pressure air to upwardly move for reposition and a head valve disposed on top of the movable cylinder.
A typical pneumatic nail gun has a gun body, a main air housing formed in the gun body to continuously collect the compressed high pressure air for nail hitting, a movable or fixed cylinder disposed in the gun body, and a hitting piston installed inside the cylinder and divided the cylinder into a top and a bottom cylinder chambers. Moreover, a trigger disposed on the gun body may be pressed to have the high pressure air guided into the top cylinder chamber to drive the piston downwardly move for hitting the nails, and be released to have the high pressure air discharged from the top cylinder chamber and guided into the bottom cylinder chamber to upwardly move the piston for reposition.
The related arts, such as U.S. Pat. No. 4,784,308, U.S. Pat. No. 4,319,705 and U.S. Pat. No. 4,294,391 respectively disclose a pneumatic nail gun having the movable cylinder and the head valve individually disposed on top of the movable cylinder. The head valve can push the cylinder moving downwardly and move upwardly together with the cylinder. When the trigger is pressed, the high pressure air in the main air housing can drive the head valve upwardly move together with the cylinder to open a bottom passage for air discharging in the bottom cylinder chamber and open the passage between the head valve and the cylinder to guide the high pressure air into the top cylinder chamber for driving the piston move downwardly. When the trigger is released, the cylinder moves downwardly together with the head valve to open a top passage for air discharging in the top cylinder chamber so that the piston can move upwardly to reposit. However, since the head valve is separated from the cylinder, in order to effectively control the head valve and the cylinder moving together, not only a passage for moving the head valve has to be formed in the gun body, but also a passage for the high pressure air moving the cylinder has to be formed in the main air housing. As such, the nail gun has a high manufacturing cost and complicated air flow passage distribution.
Above related arts also disclose to utilize a valve control device between the main air housing and the bottom cylinder chamber to control the timing of the high pressure air driving the piston move upwardly to reposit; therefore, as the trigger is released, the valve control device can open the passage between the main air housing and the bottom cylinder chamber so that the high pressure air can be continuously introduced to the bottom cylinder chamber to move the piston upwardly for reposition. However, the valve control device has complicate assembly and more passages in the nail gun are needed, as well as the valve control device is installed farther away from the cylinder in the gun body so that larger capacity of gun body and higher cost are inevitable.
Accordingly, what is needed is a pneumatic nail gun that can overcome the above-described deficiencies.